Hi scyfris,
I attempted to reproduce this following your steps but I was unable to get your results. I was able to drag around the blueprint editor correctly.
I noticed in your dxdiag that your graphics card driver looks to be out of date. Maybe try updating to see if that makes a difference.
I also noticed that you are using 2 different monitor models. Sometimes that can cause odd little issues that are hard to track down. Was the blueprint editor window located on a different monitor than the editor when the issue occured? I tried both on my system but I still couldn’t get the issue to occur. Do you have another system that you can test the issue on?